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Science 2 June 2006:
Vol. 312. no. 5778, pp. 1338 - 1341
DOI: 10.1126/science.1125731
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Reports

X-ray Fluorescence Spectrometry of Asteroid Itokawa by Hayabusa

Tatsuaki Okada,1,2* Kei Shirai,1 Yukio Yamamoto,1 Takehiko Arai,1,3 Kazunori Ogawa,1,4 Kozue Hosono,1,2 Manabu Kato1,2,4

X-ray fluorescence spectrometry of asteroid 25143 Itokawa was performed by the x-ray spectrometer onboard Hayabusa during the first touchdown on 19 November 2005. We selected those data observed during relatively enhanced solar activity and determined average elemental mass ratios of Mg/Si = 0.78 ± 0.09 and Al/Si = 0.07 ± 0.03. Our preliminary results suggest that Itokawa has a composition consistent with that of ordinary chondrites, but primitive achondrites cannot be ruled out. Among ordinary chondrites, LL- or L-chondrites appear to be more likely than H-chondrites. No substantial regional difference was found on the asteroid surface, indicating its homogeneity in composition.

1 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan.
2 Department of Earth and Planetary Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan.
3 Department of Space and Astronautical Science, Graduate University for Advanced Studies, Sagamihara, Kanagawa 229-8510, Japan.
4 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152-8550, Japan.

* To whom correspondence should be addressed. E-mail: okada{at}planeta.sci.isas.jaxa.jp

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Touchdown of the Hayabusa spacecraft at the Muses Sea on Itokawa..
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